“Geoff sustained a mild concussion during a contact session this afternoon and will undergo the recommended graduated return to play protocol” said England head coach Stuart Lancaster.

“As such, he will be unavailable for Saturday’s game but will stay in camp with a view to returning to training next week.”

It’s the second big blow for England as earlier a second Lions star, giant loose head prop Alex Corbisiero, was also ruled out of the London showdown with a knee injury.

Add to that the fact that England are also minus three other Lions stars - the rampaging Manu Tuilagi, centre partner Brad Barritt and flanker Tom Croft – and the Wallabies might start to feel quietly confident about this Saturday.

England are downplaying the loss of Parling and Corbisiero, choosing instead to highlight the fact that brothers Mako and Billy Vunipola will appear together in a Test match squad for the first time.

The Saracens duo are among 23 players that have been retained by Lancaster and will stay at Pennyhill Park to make final preparations for the weekend.

Twelve other squad members have been released to their Aviva Premiership clubs for the latest round of domestic competition.

Scrumhalf Danny Care is among that group, and will return to Harlequins to leave Lee Dickson and Lions No.9 Ben Youngs in contention for the number nine shirt.

After a brace of tries against Saracens in a recent Premiership encounter, Northampton flyer Ben Foden has forced his way into the 23, where he is joined by London Irish winger Marland Yarde, Saracens wing Chris Ashton and Harlequins fullback Mike Brown as the back-three options.

Lancaster remained upbeat about the limited options at his disposal.

“It’s never easy deciding who to select and that’s what you want – players pushing hard for places across the board” he said.

“We have had two good days of training here at Pennyhill Park and, added to last week in Leeds, we are in good form and looking forward to the game."

England Squad to face the Qantas Wallabies

Forwards (13)

David Attwood (Bath Rugby)

Dan Cole (Leicester Tigers)

Dylan Hartley (Northampton Saints)

Joe Launchbury (London Wasps)

Courtney Lawes (Northampton Saints)

Joe Marler (Harlequins)

Ben Morgan (Gloucester Rugby)

Chris Robshaw (Harlequins)

Billy Vunipola (Saracens)

Mako Vunipola (Saracens)

‘David Wilson (Bath Rugby)

Tom Wood (Northampton Saints)

Tom Youngs (Leicester Tigers)

Backs (10)

Chris Ashton (Saracens)

Mike Brown (Harlequins)

Lee Dickson (Northampton Saints)

Owen Farrell (Saracens)

Toby Flood (Leicester Tigers)

Ben Foden (Northampton Saints)

Joel Tomkins (Saracens)

Billy Twelvetrees (Gloucester Rugby)

Marland Yarde (London Irish)

Ben Youngs (Leicester Tigers)

Alex Corbisiero (knee) and Geoff Parling (mild concussion) will also return to camp for continued treatment.

The following players have been released back to their Aviva Premiership clubs (11):